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Search for the Lepton Flavor Violating Decay m  e g in the MEG Experiment

Search for the Lepton Flavor Violating Decay m  e g in the MEG Experiment. Shuei YAMADA ICEPP, University of Tokyo for the MEG collaboration. Contents. Physics Motivations Event Signature The MEG Experiment Schedule Summary. Physics Motivation.

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Search for the Lepton Flavor Violating Decay m  e g in the MEG Experiment

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  1. Search for the Lepton Flavor Violating Decay meg in the MEG Experiment Shuei YAMADA ICEPP, University of Tokyo for the MEG collaboration Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  2. Contents • Physics Motivations • Event Signature • The MEG Experiment • Schedule • Summary Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  3. Physics Motivation • meg : Lepton Flavor Violating process • Forbidden in the SM • Sensitive to new physics • SUSY GUT • SUSY Seesaw • Sensitivity • down to ~10-14 • Present limit <1.2x10-11 (MEGA) J.Hisano et al., Phys.Lett.B391 (1997) 341 Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  4. Polarized beam to measure angular distribution • Might be able to distinguish models of GUT 95.4% 90.0% 68.3% A = (|AL|2-|AR|2)/(|AL|2+|AR|2) Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  5. meg vs.tmg • B(meg)/B(tmg) = 10-3~10-4 • meg comparable to (or better than) tmg tmg meg BR BR 10-11 10-7 Expt’l bound (Belle) Expt’l bound (MEGA) 10-9 10-13 10-11 10-15 J.Hisano et al., Phys.Rev. D59 (1999) 116005 Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  6. Event Signature • Clear 2-body decay • Back to Back • Ee=Eg=52.8MeV • Backgrounds • Accidental overlap of • e+from Michel decay : menenm • gfrom radiative decay,e+-annihilation in flight • Radiative m+ decay: menenmg Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  7. The MEG Experiment • Approved at Paul Scherrer Institut, Switzerland in 1999 • Start physics run from 2006 • Initial aim at 10-13, eventually down to 10-14 Paul Scherrer Institut Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  8. The MEG Collaboration ICEPP, University of TokyoY. Hisamatsu, T. Iwamoto,T. Mashimo, S. Mihara, T. Mori, H. Natori, H. Nishiguchi, W. Ootani, K. Ozone, R. Sawada, Y. Uchiyama, S. Yamada, S. Yamashita KEK, TsukubaT. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Kasami Waseda UniversityT. Doke, J. Kikuchi, T. Kotajima, S. Suzuki, K. Terasawa, A. Yamaguchi INFN & Genova UniversityS. Dussoni, F. Gatti, D. Pergolesi, R. Valle INFN & Lecce UniversityS. Spagnolo, C. Chiri, P. Creti, M. Panareo, G. Palama’ INFN & Pavia UniversityA.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN Roma I D. Zanello INFN & Pisa UniversityA. Baldini, C. Bemporad, F. Cei, M. Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli PSI, VilligenJ. Egger, P.-R. Kettle, M. Hildebrandt, S. Ritt Budker Institute, NovosibirskL.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov, Yu. Yuri Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  9. The MEG Detector Timing Counter Compensation Coil Drift Chamber COBRA Magnet LXe Scintillation Detector 252cm Surface m+ beam (DC)～0.25x108 /sec 262cm Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  10. The MEG Detector • Most intense DC muon beam (108/sec) • Gradient magnetic field e+ spectrometer • Liquid Xe scintillation g-ray detector Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  11. 3 Techniques to Enable the Experiment LXe scintillation g-ray detector COBRA magnet w/ gradient B field Most intense DC muon beam (108/sec) Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  12. PSI Proton Cyclotron Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004 590MeV > 1.8mA > 150days/year

  13. m+ Beam @ pE5 target Quadruple magnets pE5 area @PSI Beam Transport Solenoid m+ Beamline Bending magnets The MEG detector Degrader m+/e+ separator 590MeV PrimaryProton • Intense focused DC muon beam 107~8/sec, ~f2cm • Surface muon beam : 28MeV/c Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  14. COBRA Spectrometer Solenoid with a gradient filed • COnstant Bending RAdius • Independent of emission angles • e+ momentum easily used at trigger level • reconstruction • flat acceptance • Michel e+ swept out quickly • Reduce # of hits on the chamber Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  15. COBRA is already working @ PSI !! Succeeded full excitation (Apr. 2004) Gradient field profile @ 200A(full excitation : 360A) Good agreement w/ calculation ! Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  16. Drift Chamber • Conventional DC • Less materials to reduce e+ annihilation Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  17. LXe Scintillation g-ray Detector • 800 liter Liquid Xenon scintillator • high light yield : 75% NaI(Tl) • fast response : 45ns decay time • good uniformity • 850 f2” PMTs • Facing inwards like Super-Kamiokande • Directly soaked in LXe • R&D with prototype • Performance • LXe purification • Operation @ ~165K • Construction starts this year g Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  18. 100 liter Prototype • 70L fiducial volume • 228 f2” PMTs • To verify performance & operation g beam Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  19. Task of the 100L Prototype • Detector operation • Refrigerator, monitoring system, electronics, LXe purification… • Detector performance • resolution • 228 f2” PMTs • Hamamatsu R6041Q • Soaked directly into LXe • Operation @ 165K • Long term stability Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  20. LXe Purification • Scintillation light absorbed by H2O & O2 • Achieved absorption length > 100cm (<100ppb level) After purification Before purification Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  21. Laser Compton g-ray Beam Test Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  22. Laser Compton g-ray Beam Test Inverse Compton g Energy : 10, 20, 40 MeV Incident position : detector center Estimate energy resolution using Compton edge 40MeV g Vertex distribution 40MeV Compton edge g Energy 1.6% ins 3.8mm ins Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  23. CEX p0 Beam Test @ PSI • p- beam • CEX @ Liquid H2 stopping target • Back-to-back 2g • 8x8 NaI array • opposite detector • opening angle • energy • Sep-Dec 2003 Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  24. CEX p0 Beam Test @ PSI • Monochromatic g • 55 & 83MeVp- (at rest) + pp0 + np0 (28MeV) g + g (back-to-back, 54.9MeV<Eg<82.9MeV) • 129MeVp- + pn + g • Neutron response 170°175° 54.9MeV 82.9MeV 80 Energy (MeV) 55 155 180 55 80 Opening angle(deg) Energy (MeV) Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  25. Event Display Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  26. p0 Event Sample p-pnp0,p02g Number of p.e. in Xenon p-png Energy of NaI (MeV) Number of p.e. in Xenon Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  27. Energy Spectrum @ 55MeV g • Edge resolution is important to discriminate BKG • Excellent energy resolution 4.5% FWHM Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  28. Energy Resolution preliminary 4.0 3.0 TERAS data PSI data Resolution (right s)[%] 2.0 1.0 Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  29. f2" PMT (Hamamatsu R6041Q) • t2.5mm Quartz window  Sensitive to VUV (178nm) • Photocathode : Rb-Cs-Sb w/ Mn layer  low resistance @ 165K • Q.E. : 6% in LXe (incl. Collection eff.) • Gain : 106 @ 900V • Metal Channel Dynode thin and compact • 3-atm pressure proof • TTS 750psec • Works stably within 0.5% fluctuation @ 165K 32 mm 57 mm Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  30. Further Improvement Expected • Improved PMT : Hamamatsu R9288 • Standard Bi-alkali : Sb-K-Cs • No Mn layer • Al strip patternto fit with dynode pattern • ~3-4x Q.E. improvement • Uniform Q.E. • Old PMTs ware used in 100L prototype Al strip Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  31. Another CEX p0 Beam Test • Test for • improved PMTs : ~100 improved + ~100 old PMT • Final electronics & trigger setup • 2004 Oct- @ PSI Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  32. Expected BKG & Sensitivity • Expected detector resolution • DEg : 4.5% (FWHM) • DEe : 0.8% (FWHM) • Dqeg : 18mrad (FWHM) • Dteg : 141ps (FWHM) • Expected BKG rate @ initial phase • Accidental BKG : down to ~10-14 • Radiative m+ decay : down to <10-14 • Single event sensitivity • B(meg) ~10-13 • Eventually down to 10-14 w/ improved PMTs, etc. Experimentally verified by prototype Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  33. Schedule • 2004 Oct-Another CEX beam test for LXe prototype @ PSIw/ new PMTs (~100 new & ~100 old PMTs) • mid 2005finish detector components construction • 2005-detector integrationengineering run • 2006-physics run Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  34. Summary • The MEG experiment will search for a Lepton Flavor Violating process m+e+g with sensitivity down to 10-14 • Under construction at PSI, Switzerland • COBRA magnet is ready • 100L prototype LXe g detector • Has been tested around 52.8MeV • Excellent energy resolution @ 55MeV • Beam test w/ new PMTs (2004 Oct-) • Physics run will start in 2006 Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  35. End of Slides Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  36. Electronics & Trigger • Domino Ring Sampling chip • Waveform digitizer • sampling up to 4.5GHz • 10ch x 1024bins • Readout speed up to 100MHz • Expected trigger rate : 20Hz • Photon energy >45MeV • Photon-positron timing correlation < 20ns • Photon-positron opening angle ~ 180deg. Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  37. Gas return To purifier Circulation pump Purification System • Xenon extracted from the chamber is purified by passing through the getter. • Purified xenon is returned to the chamber and liquefied again. • Circulation speed 5-6cc/minute • Enomoto Micro Pump MX-808ST-S • 25 liter/m • Teflon, SUS Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

  38. Single Event Sensitivity • B(meg)=1/{Nm T (W/4p) eeegesel}=4.5x10-14 • Nm=0.25x108/sec, T=2.6x107 sec, W/4p=0.09, ee=0.90, eg=0.6 and esel=0.7 Shuei YAMADA, ICEPP, University of Tokyo @ tau04 Nara, Sep. 15, 2004

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